Patent GB-582325-A (GB)
Title: Improvements in or relating to radio apparatus for locating distant bodies
IPC: G01S13/42
Filed: 1942-03-24
Abstract: 582,325. Radiolocation; thermionic valve circuits ; automatic volume control. COCKCROFT, J. D., and POLLARD, P. E. March 24, 1942, No. 3928. [Class 40 (v)] In a pulse radar system three different receiving aerials are provided, one for range, a differential system for bearing and a second differential system for elevation and the echo signals are fed to separate cathode-ray tubes with a common control indicating range, bearing and elevation respectively. The transmitting and receiving aerials are rotated separately, the alignment between them being indicated by a selsyn or similar indicator. Horizontal dipoles are used with telescopic ends and matching stubs to cover a frequency range of 55- 85 Me/s. Type A presentation is used on the three indicator tubes and circuits are described for wobbling the pulse recurrence frequency to avoid jamming, restricting the display on the bearing and elevation tubes to selected echoes and applying A.V.C. only to selected echoes. General operation, Fig. 4 and Fig. 2 (not shown). When searching the transmitter radiates from a single dipole, but when a target is located the transmitter output is switched to a four-bay single-stack array with a wire netting reflector, Fig. 2 (not shown). At the receiver, the echo signals received by the single range dipole are fed to the range tube R where the range is determined by shifting the trace by a calibrated range potentiometer until the echo under observation is in line with a central reference mark as described in Specification 582,170. The bearing aerial system comprises two horizontally spaced dipoles mounted in the same vertical plane as the range dipole, the outputs from which are combined in anti - phase so that the direction of zero pick-up is the same as the direction of maximum pick-up of the range dipole. The resultant output from the bearing aerials is alternately combined in phase and anti-phase with the range aerial pick-up by means of the aerial switch and the resultant alternate signals are slightly displaced vertically on the vertical trace of the bearing tube by applying a shift voltage during one signal which is controlled by the switch K ganged to the aerial switch, the system being on target when the two responses are of equal amplitude. To facilitate observation the screen of the tube is viewed through a stroboscopic disc with differently coloured windows, the disc being synchronized with the aerial switch so that the displaced responses appear to be differently coloured. The elevation aerial system comprises two vertically spaced dipoles connected to the field coils of a goniometer so that the angular position of the rotor for zero output is a function of the elevation since the vertical polar diagrams of the two dipoles are different. Since this relationship is non-linear a correcting cam is interposed between the goniometer shaft and the elevation indicator. The zero output condition is determined by combining the output from the rotor with the range aerial pick-up as in the bearing determination, the resultant signals being displayed on the elevation tube E. The traces of the bearing and elevation tubes are normally blacked out and are rendered visible by a brilliance pulse from the signal selector circuit controlled by a potentiometer ganged to the range potentiometer so that only responses corresponding to the target under observation are displayed ; these visible responses are in the centre of the traces since the tubes are fed from a common time-base with a shift potentiometer ganged to the range potentiometer. When searching for a distant object, the top elevation dipole is used in place of the range dipole a reflector being provided to determine " sense ". Modulator, Fig. 3, and transmitter, Fig. 2 (not shown). The pulse recurrence frequency is determined by the blocking oscillator V3, the frequency of which is controlled by the damping resistance R10 across the primary of transformer T2 and also wobbled at a rate determined by the blocking oscillator V1 which produces a saw-tooth output which is fed through the cathode follower V2 to the cathode of V3. The positive square-wave output from V3 is converted into sharp positive pulses by the shaping circuits V4 and V5 and applied to the parallel cathode followers V6 and V7, the cathodes of which are directly connected to the grids of the RF oscillators. The cathodes of V6 and V7 are also returned to a -1000V line so that when the valves are non-conductive the oscillators are biassed off, but the bias is removed when the valves become conductive due to the positive triggering pulse. Fluctuations of the bias voltage are prevented by the gas discharge tube V10 and voltage surges due to flash-over in the RF oscillator are by-passed by the gas-filled diode V9. A time-base voltage for a monitor cathode-ray tube is generated by V8 which is fed with negative pulses from V4 and positive brilliance pulses to brighten the forward stroke of the time base are developed across the resistance R10 in the cathode circuit of V6 and V7. The transmitter, Fig. 2, comprises a pair of push-pull connected triode oscillators with lecher tuned grid and anode circuits, the duration of the pulse being determined by a grid squeg circuit. The output is tapped off from the tuned cathode circuit and tapped into the tuned cathode circuit of the push-pull output triodes, the anodes of which are tuned by a Lecher line provided with tappings for the output to the aerial. The output is also fed to the monitor tube through delay and attenuation networks. The anodes of the oscillator and output valves are supplied from reservoir condensers connected to the H.T. rectifier through limiting resistances and negative output locking pulses are produced across a resistance connected between earth and the " earthy " end of the output stage reservoir condensers. Receiver, Figs. 5 and 6 (not shown). The R.F. amplifier comprises five tuned-grid stages with ganged tuning an A.V.C. control voltage being applied to the grids of the last three stages ; the R.F. output is fed to the anode of a diode mixer and the output from the local Hartley oscillator is fed to the mixer cathode. The I.F. output from the mixer anode is fed through a filter to the I.F. amplifier, an additional tunable filter being provided to eliminate C.W. interference. The I.F. amplifier comprises five tuned-grid stages with staggered tuning the output being fed to a diode detector feeding two output stages in parallel, one of which feeds the range tube and the other the bearing and elevation tubes; the A.V.C. control voltage is also derived from an output taken from the latter stage. Time-base circuits. In the range time-base circuit, Fig. 8 (not shown), the negative locking pulses from the transmitter are fed to the cathode of a grounded grid " locking " valve V30, the anode of which is directly coupled to one anode of a multi-vibrator V31 and V32 giving a negative square wave output which cuts off the time-base valve V23 allowing a condenser to charge through a resistance from a 4000V source ; this voltage may be reduced to 1000V to increase the time base range. An output from the multi-vibrator is also fed to another valve V33 to give a positive brilliance pulse for the range tube, and other outputs are fed to the common bearing and elevation time base, Fig. 7 (a) (not shown), and the signal selecting circuit, Fig. 7 (c). Signal-selecting circuits, Figs. 7 (c) and 9. The circuit of V24, Fig. 7 (c), generates a sawtooth voltage in a similar manner to the range time-base generator and the H.T. supply for the circuit is earthed through the slider S3 and the cathode follower V29 which forms part of a potentiometer guard circuit similar to the one used with the range potentiometer in the Specification referred to. The saw-tooth output is thus variable about earth potential by the slider S3 which is ganged to the range potentiometer and this output is fed to the grid of V34, Fig. 9, to give a negative waveform with a variable leading edge which is applied to the shaping circuit V35 to give a variable-position positive selector pulse which is fed through the terminal 17 to the grids of the bearing and elevation tubes. Output signals from the receiver are fed through V36 to the grid of a gate valve V37 which is " opened " by the selector pulses fed to its suppressor grid. The selected signals are D.C. restored by the diode V38 and rectified by the diode V39 to give an A.V.C. control voltage, a delay voltage being developed across the resistance R31. Calibrator circuit, Fig. 10 (not shown). The output from a crystal controlled oscillator V42 is applied to a gate valve V43 controlled by the output from a blocking oscillator V44 to give discrete trains of sinusoidal oscillations which are applied to the Y-plates of the range tube and also fed to trigger the range time-base.